Quantum information processing uses quantum mechanical effects to store and process information in the form of quantum bits or “qubits”.
Different types of systems have been proposed which can implement a two-level system which can be used as a qubit, such as ion traps, dopant impurities, superconducting devices and quantum dots.
An isolated double quantum dot may be used to provide a charge qubit which can be initialised and manipulated using capacitively-coupled gates and using a capacitively coupled single-electron transistor, as described in J. Gorman et al: “Charge-Qubit Operation of an Isolated Double Quantum Dot”, Physical Review Letters, volume 95, page 090502 (2005). Quantum dots can also be used to provide other types of qubits, such as spin qubits. Although quantum dot-based quantum information processing offers many advantages, current quantum dot-based systems tend to fall short of providing a practical system. For example, there tend to be limits as to how the number of qubits system can be scaled up while also allowing easy initialisation, manipulation and read out.
Silicon nanowire field-effect transistors are being investigated as a possible system for implement spin and charge qubits. For example, B. Voisin et al.: “Few-Electron Edge-State Quantum Dots in a Silicon Nanowire Field-Effect Transistor”, Nanoletters, volume 14, page 2094 (2014) describes a silicon nanowire field-effect transistor which forms edge states which can be localised into quantum dots to provide spin qubits. M. F. Gonzalez-Zalba, S. Barrud, A. J. Ferguson and A. C. Betz: “Probing the limits of gate-based charge sensing”, Nature Communications, volume 6, page 6084 (2015) describes a silicon nanowire field-effect transistor which forms a double quantum dot system and high-sensitivity gate-based detection change sensing system. However, in these devices, control over the quantum dots is restricted which can limit how a qubit is initialised, manipulated and read out.